Principles of Top-Down Mixed-Signal Design
Many design groups currently claim to be following a top-down design process, yet experience most of the problems attributed to the use of a bottom-up design style. This is because they are basically employing a bottom-up style with a few relatively cosmetic changes that serve to give the appearance of top-down design. This paper lays out a series of principles that must be followed to realize all of the benefits associated with a rigorous top-down design methodology.
A rigorous top-down design methodology requires a significant investment in time and training and a serious commitment throughout the design process if it is to be success- ful. However, it is much easier the second time around and once mastered provides dra- matic returns. Fewer design iterations and silicon respins are needed, which results in a shorter and more predictable design process. More optimal designs are produced that are better verified. It allows design teams to be larger and more dispersed, giving the option of trading a higher initial investment rate for a shorter time-to-market. And it is relatively tolerant of changes in the requirements that occur late in the design cycle.
Employing a rigorous top-down design methodology dramatically increases the effec- tiveness and productivity of a design team. If a design team fails to move to such a design style while its competitors do, it will become increasingly ineffective. It eventu- ally will be unable to get products to market in a time of relevance and so will be forced out of the market.
Given the high pressure world that most designers live in, it is difficult for them to acquire the skills needed to be successful in a rigorous to-down design methodology. In addition, there is little training available from continuing education centers. This sug- gests that the transition to top-down design will be slow. The best hope for accelerating the move to top-down design is for universities to give designers the necessary back- ground and training in the benefits and practice of rigorous top-down design. There are some signs that this is beginning , but it is not as aggressive or as widespread as it needs to be in order for there to be a smooth and timely transition.
If You Have Questions
If you have questions about what you have just read, feel free to post them on the Forum section of The Designer’s Guide Community website. Do so by going to www.designers- guide.org/Forum.
Much of the material presented is based on discussions with Dan Jefferies, Henry Chang and Alessandro Piovaccari of Cadence Design Systems and Jim Holmes of Texas Instru- ments.
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